Treatment of wells



Jan. ,4, 1938.

H. T. KENNEDY ET AL TREATMENT OF WELLS Filed Oct. 3, 1955 'um' l '"h.. IIE! MMIII) l l Zahmkhw o KN ,dzmzwu NVN WN @N aN www# Enamww Mm?? a ZHZHO m Ww WNN .zag

Patented Jan. 4,1938

2,104,488 i TREATMENT or WELLS Harvey T. Kennedy, Forest Hills,

Wescott, Oakmont, Pa., assignors to and Blaine B.

Gulf Research & Development Company, a corporation of Delaware Application October 3, 1935, Serial No. 43,440

' inert suspension adapted to form a gel on stand- 6 Claims.

This invention relates to treatment of wells; and it comprises a method of selectively sealing or solidifying water bearing strata in wells which penetrate such strata and which also penetrate underlying strata which it is desired not to treat; the method comprising the steps of introducing into the well a body of a suspension forming a gel-like mass up to a level adjacent but below the level to be sealed or solidified, and then intro- 10 ducing sealing or solidifying agents into the well and surrounding formations, the agents being prevented by a gel-like mass from penetration into the strata which it is not desired to treat; all as more fully hereinafter set forth and as claimed. Oil wells often pass through water bearing formations: shifting sands 'or pervious rock bearing flowing water or brines'. It is usually essential to restrain or shut off these formations. Inflow of water to a well either during drilling or production is undesirable for many reasons.

In the past, when a water bearing formation was encountered during drilling, the usual procedure was to drill beyond the water-producing stratum, run in casing, cement or pack it off and proceed Witha drill of smaller diameter. This procedure required that an additional inner string or smaller diameter casing be employed each'tiine the diameter of the bore was diminished, making it an extremely expensive operation Recently, however, there have been developed chemical methods of sealing or plugging such water-bearing formations by impregnation. These involve injecting one or more relatively mobile solutions or suspensions of agents which give an insoluble precipitate, clot or coagulum of some sort in ,the water stratum. Such methods obviate the necessity for running a casing prematurely.

Chemical shut-off methods have also been employed for shutting off water in the uncased portion of completed Wells.

One disadvantage of such procedures is that when the strata to be sealed are located not at the bottom of the well but some distance above, as is often the case, excessive quantities of solutions have been required; and the plugging solution standing in the Well below the level under treatment does no good and may obstruct underlying oil bearing strata. Y Waste occurs. This is true both in wells being drilled and in completed wells.

The present invention presents an improvement upon such procedures. According to the invention the well is first `partly filled with an ing in the well. Or the gel is formed inthe Well by inserting dry gel-forming materials and then adding water. Enough gel is provided to shut oil the lower portions of the well up to the level 5 under treatment or at least enough to close off underlying strata such as oil strata which it is desired not to plug permanently. Then there is injected a suitable sealing agent. The gel forms in effect a so1id` table or column which 10 effectively prevents waste of any sealing -agent by penetration into the well below the desired level. When there are oil bearing strata below the water layers, as is often the case, the gel body temporarily closes olf such strata'and prevents any kplugging action thereon. After the 'sealing operation is finished, the gel body can be withdrawn, leaving the oil strata exposed.

The most useful gel for our purpose, on the whole, is one made from bentonite and water. 20 Auid suspension can be made from bentonite which is readily pumped and piped but which sets on standing to a firm gel. Such a gel has thixotropic properties; while undisturbed it has almost a solid or rigid character, but on agita- 25 tion as by pumping or hailing it turns freely liquid. A suspension of 3 to 5 parts commercial bentonite in 100 parts Water is satisfactory. Organic gel forming materials can be used, such as aqueous starch gel, if desired.

The sealing agent for the water bearing layers can be of one of several different types. A particularly good sealing agent is silicon tetrachlorid, either in its pure (liquid) state or in oil solution. Such solution can be readily injected far into porous formations bearing water. Gradual interaction with the water occurs, with the development of a bullq7 precipitate of hydrated silica. Other good sealing agents are watersoluble soaps of a type adapted to give a precipi- 40 tate in local waters; e. g. rosin size.

Inlan example of one specific embodiment of the invention, an oil Well of depth 5000 feet, of which the last 300 feet is uncased, has an oil producing stratum near the bottom and a Water bearing stratum 200 feet above the bottom at the 4800 foot level. It is required to shut off the Water stratum. According to the invention there is made up a batch of bentonite suspension suicient to fill the well up to just below the level of the water stratum. The suspension is pumped in and allowed to assume a solid state. Then there is injected far into the water formation, by pumping under high pressure, a solution of l5 parts silicon tetrachlorid in parts oil (by 55 weight).

In the presence of water, the silicon tetrachlorid is decomposed with the formation of a. bulky precipitate oi hydrated silica, which effectively plugs the pores of the water formation. Then the bentonite body is removed by hailing or pumping, leaving the oil stratum exposed and free to produce.

Sometimes the (metal)l casing of an oil well becomes perforated through corrosion and water enters the casing through the perforations. These perforations may occur a long distance from the bottom of the well. In such instances, the interior of the casing is iilled with gel body to a point adjacent and below the point of water intrusion. The sealing agent is then introduced into the interior of Vthe casing `and forced out of the perforations and into the water-bearing stratum by application' of pressure at the casing head.

When the well to be treated is uncased in the region to be treated, the sealing agent is merely introduced above the gel body.

Typical applicationsl of the method of the invention are illustrated in the accompanying dlagrammatic drawing, in which:

Fig. 1 shows the application of the invention' in sealing off a water stratum in the uncased portion of a completed well, the uncased portion having a water producing. stratum overlying an oil producing stratum and Fig. 2 shows the application of the invention in sealing ofl'- a water stratum which is adjacent the cased portion of an oil well, the casing having been perforated by corrosion to such an extentvas to permit intrusion of water.

Referring to Fig. l, reference characterv l indicates the upper portion of lthe bore of an oily well having a. casing 2 resting on a rock-shoulder 3 of the bore I. Adjacent the bore l are rock strata 4 and a. water bearing stratum 5 interposed therebetween. In accordance with the known practice, casing 2 is cemented as at S to prevent intrusion of water from stratum 5. Beneath the upper portion I of the bore is an uncased portion 'I penetrating, in downward order, an unirm or shifting stratum 8, a water bearing stratum il, a firm stratum l0, 4and an oil producing stratum II. When the well was first completed, stratum 9 produced oil; hence the well was not cased below the point shown. However, owing to ther formation in stratum 9 having greater permeability than that in stratum Ii, the oil originally present ln exhausted and water is now` entering the well bore through the latter stratum. Stratum Il is still producing oil,'and it is desired to shut oli the flow of water from stratum 9.

In accordance with the present invention, the bore l is filled up to a point below and adjacent stratum Il with a body of gel I 2. There is then introduced above the gel body I2 a charge of plugging agent I3, the plugging agent being accurately positioned and 4held at the desired location by virtue of being supported on the gel body. Pressure is applied to the charge i3 from above, as by a column of oil, to force the plugging agent into the water bearing stratum 9. When the plugging action is complete, the gel charge I2 is pumped or bailed out, leaving the oil stratum II free to produce, while the Water stratum is left effectively plugged.

Referring to Fig. 2, the upper portion I of an old oil well is shown having a casing section 2 resting on a shoulder 3. Adjacent the portion I are shown rock strata 4 and water-bearing strastratum 9 has been l water into the well.

tum 5 interposed therebetween. Casing 2 has `been cemented as at 6 to prevent intrusion ci water and is still sound and impermeable. Below upper portion I of the well bore is shown an intermediate portion I4 of smaller diameter. Bore id passes throughv a.l second water bearing stratum i5 and is cased by an inner string of casing it resting on a shoulder Il and cemented as at I8. Beneath the shoulder il the bore is of even smaller diameter and is uncased to permit ingress of oil from formation il. As illustrated, the inner string of casing I6 has become perforated by corrosion at the level of water stratum I5 and water is entering the casing through the periorations i9.

-In accordance with the present invention, enough gelbody I2 is introduced into the well to entirely :dll bore l and, in addition, to iill enough of bore I4 to bring the upper level of the gel body immediately below and adjacent perforations I9. There is then introduced above the gel body I2 a charge of plugging agent i3 and pressure is applied to drive the plugging agent through perforations I and into water bearing stratum i5. When the plugging action is complete, the gel body is removed by hailing or pumping. l

The invention is also applicable to drilling operations when, during drilling, avwater stratum is passed and the flow from this stratum is not prevented ror counteracted by the hydrostatic pressure of the drilling mud column. This condition is not always recognized until the bore has progressed considerably beyond the water-bearing stratum. Often, such water is highly corrosive and therefore damaging to the drill pipe. Also, when entering the bore in large quantities, water makes it impossible to keep the drilling mud proper consistency.

In such instances, application of this invention is desirable and advantageous in conserving plugging agent and in preventing application oi plugging agents to portions of the bore not desired to be treated therewith.

What we claim is:-

. 1. A method of selectively sealing or solidifying water-bearing stratav by impregnation in wells penetrating suchv strata and also penetrating lower, cil-bearing strata, which comprises establishing in the well a body of gel extending up adjacent but below the water strata and closing off the oil strata, injecting a liquid sealing agent into the well above the gel body and forcing the sealing `agent into the water-bearing strata to impregnato said strata and seal them, the sealing agent being prevented from entering the oil strata. by the gel body, and then removing the gel body, leaving the oil strata exposed.

2. The method of claim 1 wherein the body of gel is aqueous bentonite gel.

3. The method of claim 1 wherein the sealing agent is silicon tetrachlorid in liquid condition.

4. The method of claim 1 wherein the sealing agent is a solution of rosin size.

5. A method of sealing a water-bearing formation in wells having a. casing perforate adjacent the water-bearing formation and through which water leaks into the well, which comprises establishing in the well a body of gel extending up to adjacent but below the perforate portion of the casing, injecting a liquid sealing agent into the well above the gel body and forcing the sealing agent through the perforations 4into the adjoining formation to prevent further leakage of 6, A method of selectively sealing or solidifying water-containing strata in wells. the watercontaining strata. occurring at a level above the bottom of the well, which comprises establishing in the well a body of gel extending from the bottom of the well up adjacent but below the water-containing strata. and injecting a liquid sealing agent unde' high pressure into the water bearinsstratatoimpregnatc saitlstrata'and` seal them, the sealing agent being localised at the water-containing strata through the agency o! the gel body.

HARVEY T. KENNEDY. BLAINE B. WESCOTT. 

